The present invention relates to a method and equipment for measuring the deformation of a reflector; and more generally, the invention relates to measuring deformation of wavefronts on an interferometric basis.
The deformation of an optical surface can be measured interferometrically, using, for example, an interferometer as disclosed in U.S. Pat. No. 4,188,122 by me and another. This device was designed primarily for purposes of enhancing optical phase and spatial resolution of the measurement. Thus, this device depends to a great extent upon the utilization of a large number of detect points. In fact, it is the advantage of that device that it permits utilization of many points of detection in order to increase resolution. Inherently, the device is relatively slow in the acquisition of data by means of acquisition cycles, each of which is comprised of a sequence of interrogating steps to cover all of the detect points. One could, of course, interrogate these points in parallel, but at a prohibitive expense in equipment. On the other hand, certain optical surfaces undergo contour changes which have a relative high bandwidth.
It is, therefore, an object of the present invention to provide a new and improved method and equipment for determining the contour of an optical surface at a high speed, when deformations are dominated by, or even restricted to, a few modes with the lowest spatial frequencies.